1. Technical Field
The present invention relates to an air bag deployment system for a vehicle and a method for pre-impact deployment of the air bag.
2. Background Art
Air bag systems are widely used in the vehicle industry and have provided vehicle occupants with enhanced safety for the last decades. In an automotive vehicle it is common to position air bags in the hub of the steering wheel, in a recess in the instrument panel, in the seats, and/or in the door panels or in the A, B and C pillars. Other positions are of course also possible. In any mounting positions, the air bag is required to inflate very fast and at the correct moment.
Air bags are usually in fluid communication with a gas emitting inflator, which in turn is generally in electrical communication with an impact sensor. During e.g. a frontal collision between two vehicles, the sensor, e.g. an accelerometer, detects a very rapid deceleration immediately after the vehicle impacts another object, such as another vehicle or a fixed object. The collision generates an impact pulse which runs through the vehicle; as a consequence, occupants are thrown in the forward direction. Upon detection of the impact, the impact sensor triggers the gas emitting inflator to inflate the air bag, which restrains and cushions the occupant. It has been found that the inflation of the air bag may be varied depending upon the severity of the collision; such a system is disclosed in U.S. Pat. No. 6,454,300 B1. The system comprises a release mechanism to hold restraining air bag tethers, which can be selectively released at a predetermined condition to provide an air bag of varying size depending on the severity of the collision.
As mentioned above, an occupant is thrown forward during a frontal collision due to the impact pulse imparted by the impact. To minimize or prevent injuries to the occupants during a collision it is vital that the peak level of deceleration experienced by the occupant be kept as low as possible. The patent publication referred to above provides a system for varying the size of the air bag depending on the severity of the collision. Another air bag system, similar to the one referred to above, is disclosed in US 2007/0246924 A1. The air bag system utilizes releasable tethers which can be released at a predetermined condition. Both the documents above utilize impact sensors which detect the occurrence of an impact. Additionally in US 2007/0246924 A1, the system can be complemented with seat position sensors, an occupant position sensor, a seatbelt usage sensor or a seat weight sensor. All sensors are used to provide a degree of inflation of the air bag intended to minimize the sudden deceleration of the occupant during collision.
During a normal collision using systems as described above, an occupant's head moves about 120-130 mm (about 5 inches) from the moment of impact to the moment when the air bag is fully deployed. Further, the general deployment time of an air bag is about 30 ms (milliseconds). This ratio is also known as the 5/30 rule within the industry. Considering that the general total deceleration distance for an occupant, e.g. in the driver's seat, is about 450 mm of which only 300 mm up to this date is used, there remains a need for further improved methods and systems which soften the deceleration of the occupant and increase the deceleration distance of the occupant during impact to minimize personal injuries.